The invention relates to packet radio, particularly packet radio suitable for use in the tactical forward area of a battlefield.
Packet radio systems have been known for several years: see for example "Computer Networks" by Andrew S. Tanenbaum, published by Prentice-Hall (1981), and "Advances in Packet Radio Technology" by R. E. Kahn et al., Proc. IEEE, Vol. 66 (November 1978), pages 1468-1496. A packet radio system is a data communications radio network comprising a plurality of stations each including a transceiver. Each station can act a source, relayer or destination of a data message. A data message to be communicated is divided into discrete segments of fixed length, called "packets". The stations of a network are generally distributed over a geographical area in such a manner that not every station is in direct communication (i.e. communication without an intermediate station) with every other station. A packet therefore usually propagates from source to destination in a series of hops, being relayed by intermediate stations. The system selects an appropriate route for each packet depending upon the loading of individual stations, local interference and network topology. Each station can store a number of packets, possibly from different sources and possibly intended for different destinations, until they can each be forwarded to another station nearer to their respective destinations. Packets arrive at the destination station, possibly by different routes and not necessarily in the correct order, and are re-assembled to form the original message. When a station has received a packet, it transmits an acknowledgement of that fact, but this occurs for each hop in the propagation route: there is no automatic acknowledgement from destination to source (unless the stations happen to be in direct communication), so the network provides a so-called "unacknowledged datagram" service.
A packet radio system can provide mobile battlefield data users with a common communication service which is comparable, in terms of transparency of service and reliability, to a static trunk system. For this reason, packet radio is seen as a possible solution to the growing data communications requirements of the mobile electronic battlefield in an increasingly congested electromagnetic spectrum.
The designer of such a packet radio system is however presented with formidable problems: for example, the stations are mobile causing the network topology to change regularly, the propagation channel has a high information error rate which fluctuates with time, and any station may be switched off without notice.
It has recently been proposed (see "Packet Radio--A Survivable Data Communications System for the Forward Area" by B. H. Davies and T. R. Davies, Proceedings of the IEE Conference on Advances in Command, Control and Communications Systems: Theory and Applications, Apr. 16-18, 1985, pages 129-137 (IEE Conference Publication No. 247)) to use a fully distributed control strategy, employing robust routing and channel access algorithms, in order to provide improved performance, for example as regards reliability, in view of the above-mentioned problems; this system has been designed to operate within the constraints of existing narrow-band radio technology.
The present invention may similarly use available narrow-band radio technology but enables a packet radio system to have increased capabilities.